The cellular, biological and immunological factors in peripheral nerve regeneration are being studied in a rat vein-graft model. The vein graft serves as a chamber into which various biological agents such as collagen or "trophic" factors such as nerve growth factor as well as specific cell types grown in tissue culture can be added to study their effects on axonal regeneration. Quantitative light and electron microscopic measures are being utilized to analyze the effects. To date, certain human tumor cells in the vein-graft have enhanced regeneration whereas microcrystalline collagen has inhibited the process. The study of the influence of fetal dorsal root ganglion cells, cerebellar cells, cortical cells, and fibroblasts has continued and lectins have been added to study the role of glycoproteins in the regeneration process. A protocol (80-N-06) to study factors in failed human peripheral nerve regeneration has been in operation and the first patients have been entered and are currently under study.